A large-scale project in China demonstrates how up-to-date measuring technology can be when it is continuously developed and produced at a high quality level for five decades. When it came to the question of which slot thermometers to use in the 700-megawatt blocks of the world’s largest dam, the Three Gorges Dam in China, the focus was not on the sensors’ price, but on their quality and reliability.
In large-scale generators such as those used in the Three Gorges project, recording the precise temperature during operation is essential in order to prevent expensive damage of even the total failure of the unit. Conventional slot thermometers only record the temperature at a single point measuring around 2 x 3 mm. It is easy to imagine the problems the Chinese engineers of a 950-megawatt plant, for example, faced in finding the right installation position for the slot thermometer with only isolated measurement. It would be almost impossible to define the hot spot in advance. This would usually result in the sensor being installed incorrectly, endangering the machine due to incorrect temperature measurement or an incorrect choice of measuring point.
EPHYMESS had the solution
Using bifilar wound slot thermometers eliminates this risk. The construction of the rigid and flexible thermometers of EPHYMESS types NWT-A and NWT-SH allows a temperature-sensitive length of up to 900 mm.
In the view of the Chinese client, only one manufacturer came into question for supplying the sensors for this large-scale project – a manufacturer that had proved its quality and reliability over many years. The requirements for the slot thermometers to be delivered were tough. The following criteria ultimately decided the choice of supplier:
- Temperature sensitive length across the entire sensor
- Sensor screened against electromagnetic interference
- Sensor winding not sensitive to pressure, min. 25 kp/cm²
- High constructive tensile strength of sensor to cable of 100 N
- Materials approved for power plants
- Maximum measuring accuracy, Class A as per EN 60751
- High voltage resistance of up to 5 kV/60 sec.
Only bifilar wound slot thermometers meet all these selection criteria.
Not only slot thermometers used in dam
As well as slot thermometers, numerous other types of sensor from EPHYMESS are used in the project. The oil temperature, for example, is measured by highly vibration-resistant bearing thermometers of type EM 24 or 38 and special constructions in IP 67. EPHYMESS was chosen as the supplier of the temperature sensors not only due to the quality of the slot thermometers but also the company’s ability to implement special constructions in close consultation with the engineers on site – even on very tight deadlines. That’s just typical EPHYMESS.
